A variety of current-sensitive electromagnetic devices have been provided which are sensitive to and are indicative of the strength of an electric current. There are a variety of galvanometers that are presently in use for this purpose. One problem faced with presently available galvanometers that are used in polygraph instruments is that they are relatively expensive and require rather sophisticated electromagnetic and null structure such as torsion rods or counter-opposed springs to return the instrument to a null or zero position. Moreover, presently available galvanometers are not entirely satisfactory for use with the amplified electric signals developed in polygraph instruments.
Accordingly, it is an object of the present invention to provide a simple, durable, relatively inexpensive, and yet highly sensitive electromagnetic device.
Another object of this invention is to provide a novel and improved electromagnetic device that has adjustable sensitivity and adjustable frequency response with the capability of adjusting the device for a null or zero reference with relative ease.
Still another object of this invention is to provide a novel electromagnetic device that is compatible with the electric signals produced by the amplifier stage of a polygraph instrument.
A further object of this invention is to provide a novel electromagnetic device that virtually eliminates backlash and is highly sensitive over a wide frequency range without the use or necessity of relatively complex and costly null mechanisms.